Which command enables BFD association with OSPF across all interfaces?

The command that enables Bidirectional Forwarding Detection (BFD) association with OSPF across all interfaces is "bfd all-interface enable." This command allows the configuration of BFD for all interfaces on a device in one step, streamlining the process of enabling fast failure detection in OSPF.

BFD is used in conjunction with OSPF to provide rapid detection of link failures, which can enhance routing stability and minimize downtime. By enabling BFD across all interfaces, the router can quickly respond to a failure, allowing OSPF to reroute traffic without waiting for longer timeout periods associated with traditional link state updates.

While other options may seem plausible, they either do not explicitly express a global configuration for all interfaces or may imply toggling states rather than enabling BFD directly across the board. Therefore, "bfd all-interface enable" is the most appropriate command for the purpose stated in the question.